Oil and gas wells which are drilled offshore are normally completed above the water surface on a fixed structure. However, in some cases it is desirable to complete these wells at the ocean floor, but this generally requires the installation of special and extensive completion equipment such as described in "A Maximum Safety Platform Completion System", OTC Paper No. 1527, May, 1972, and "A Koomey-SSS System", an advertisement, date unknown.
The present invention relates to a subsea well completion system and method in which after the well has been drilled and all casing strings set, it is only necessary to disconnect the tie-back connectors and run a novel type of tubing hanger body with tubing strings supported from it. The present system does not require the use of a high cost completion housing but instead includes a tubing hanger and tree adapter which have side outlets to permit monitoring the tubing and casing annuli pressures and/or the testing of seals. The present completion system provides a selective communication with these annuli for the detection of leaks and the possibility of bleeding off the pressures and/or pumping cement or other materials through the tree adapter and tubing hanger to seal off the leaks. Also, in the United States, the abandonment of an off-shore well requires that cement be pumped into all casing and tubing string annuli as well as down the production tubing so as to completely plug any flow path from the bottom of the well to the surface. In addition, it is required that all portions of the well be removed to at least 15 feet below the ocean floor. These requirements normally necessiate the reentry into the well using a rig similar to the one that drilled the well. These operations are obviously costly as well as hazardous.
The present invention permits the monitoring of the casing and tubing annuli, both during and after completion of the well, and further permits the pumping of cement into these annuli through external outlets on the tree adapter. This makes it possible to perform abandonment operations using a work barge and divers rather than a drilling rig. After cementing, the well completion system is severed at least 15 feet below the ocean floor such as by an explosive charge. This method of abandoning the well costs only a small fraction of that required if a rig had been used.